72 



THE VERTEBRATE OVARY AND ITS RELATIONSHIP TO REPRODUCTION 



CAVITY OF FOLLICLE 



GRANULOSA CELLS 



BASEMENT MEMBRANE 

 THECA INTERNA 



CAPILLARY 

 THECA EXTERN A 





Fig. 44. Cellular wall of the mature Graafian follicle in the opossum. 



layers of epithelial or granulosa cells surrounding the egg. It may now be 

 regarded as a secondary Graafian follicle (fig. 42A, B). When a stage is reached 

 where the granulosa cells form a layer five to seven or more cells in thickness 

 extending outward from the egg to the forming thecal layers, small antral 

 vacuoles begin to appear among the granulosa cells. The latter follicle, which 

 is capable of forming antral vacuoles, may be regarded as a tertiary Graafian 

 follicle (fig. 43 A). 



4. Hormonal Factors Concerned with the Development 

 OF Egg Follicles 



The ovary with its contained egg follicles is greatly affected by the gona- 

 dotrophic hormones produced in the pituitary body. The removal of the pi- 

 tuitary body (hypophysectomy) causes profound regression of the ovary and 

 accessory reproductive structures. Accordingly, the response of the ovarian 

 tissues to these hormonal substances produced by the hypophysis is responsible 

 for development of the Graafian follicle beyond the early tertiary stage. (See 

 fig. 40A.) The relationships between the pituitary hormones and the ovary 

 have been studied most intimately in the mammals; the pituitary and egg- 

 follicle relationship in lower vertebrates is more obscure, and probably varies 

 with the particular group. 



a. Effects Produced by the Gonadotrophic Hormones on the 

 Development of the Mammalian Egg Follicle 



The follicle-stimulating hormone, FSH, appears to increase the number 

 of oogonia and to aid the growth and differentiation of the older follicles. It 

 is possible that some of the effects of FSH upon follicular growth are medi- 

 ated through its ability, together with small amounts of the luteinizing hor- 

 mone, LH (ICSH), to cause the formation of estrogen or the female sex 



